Pneumatic tire

Abstract

A pneumatic tire having an enhanced cracking resistance at groove bottom, including at least one circumferential main groove 9 having such a sectional profile shape as including an axially inner wall portion 13 , an inner arc portion 14 continuous with the inner wall portion 13 , an axially outer wall portion 15 having a smaller length than the inner wall portion 13 , an outer arc portion 16 continuous with outer wall portion 15 , and a groove bottom portion 17 extending straight between the outer and inner arc portions while being inclined in a radially inward direction, in which the groove 9 has a maximum depth portion 18 on the tire equator side with respect to center position G 1 of its width, and radius of curvature R 1 of inner arc portion 14 and radius of curvature R 2 of outer arc portion 16 satisfy the following relationships: R 1 ≧0.6 mm and R 2≧ 2×R 1.

What is claimed is: 
     
       1. A pneumatic tire comprising:
 a tread portion provided with a circumferential main groove extending in a circumferential direction of the tire at a location distant from the tire equator toward an axially outer side thereof, 
 said circumferential main groove having a profile shape such that, 
 in a meridian cross section of the tire including the rotation axis of the tire in a standard state that the tire is mounted on a standard rim and inflated to a normal inner pressure and no load is applied to the tire, 
 the profile shape includes
 an inner wall portion extending radially inwardly from an axially inner edge of the groove on a tire equator side, 
 an inner arc portion continuous with said inner wall portion and having a smaller radius of curvature than that of said inner wall portion, 
 an outer wall portion extending radially inwardly from an axially outer edge of the groove on a tread edge side and having a smaller length than that of said inner wall portion, 
 an outer arc portion continuous with said outer wall portion and having a smaller radius of curvature than that of said outer wall portion, and 
 a groove bottom portion extending straight from said outer arc portion toward said inner arc portion while being inclined in a radially inward direction, 
 
 wherein said circumferential main groove has a maximum depth portion on a tire equator side of a center position of its width, 
 
       wherein
 said inner arc portion has a radius of curvature R 1  and said outer arc portion has a radius of curvature R 2  that satisfy the following relationships:
 R 1 ≧0.6 mm, and 
 R 2 ≧2×R 1 , 
 
 
       and wherein
 on the tread edge side of said circumferential main groove, a plurality of shoulder blocks are disposed circumferentially of the tire, and 
 with respect to each said shoulder block, the radius of curvature R 2  is gradually decreased from a center portion toward both end portions of the block in the tire circumferential direction. 
 
     
     
       2. The pneumatic tire of  claim 1 , wherein the center position of the width of said circumferential main groove is located at a position apart from the tire equator by a distance of 10 to 35% of a tread width TW which is an axial distance between the tread edges. 
     
     
       3. The pneumatic tire of  claim 1 , wherein said circumferential main groove extends at an angle of 45° or less with respect to the circumferential direction of the tire.